Membrane with optimized dimensions for a fuel cell

ABSTRACT

A UEA for a fuel cell having an active region and a feed region is provided. The UEA includes an electrolyte membrane disposed between a pair of electrodes. The electrolyte membrane and the pair of electrodes is further disposed between a pair of DM. The electrolyte membrane, the pair of electrodes, and the DM are configured to be disposed at the active region of the fuel cell. A barrier film coupled to the electrolyte membrane is configured to be disposed at the feed region of the fuel cell. The dimensions of the electrolyte membrane are thereby optimized. A fuel cell having the UEA, and a fuel cell stack formed from a plurality of the fuel cells, is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/020,275 filed on Feb. 3, 2011 which is a divisional of U.S. patentapplication Ser. No. 11/972,211 filed on Jan. 10, 2008. The entiredisclosures of the above applications are hereby incorporated herein byreference.

FIELD OF THE INVENTION

The present disclosure relates to a fuel cell and, more particularly, toa fuel cell unitized-electrode-assembly (UEA) having an electrolytemembrane with optimized dimensions.

BACKGROUND OF THE INVENTION

A fuel cell has been proposed as a clean, efficient and environmentallyresponsible power source for various applications. In particular,individual fuel cells can be stacked together in series to form a fuelcell stack capable of supplying a quantity of electricity sufficient topower an electric vehicle. Accordingly, the fuel cell has beenidentified as a potential alternative for a traditionalinternal-combustion engine used in modern vehicles.

A common type of fuel cell is known as a proton exchange membrane (PEM)fuel cell. The PEM fuel cell includes three basic components: a cathodeelectrode, an anode electrode, and an electrolyte membrane. Theelectrodes typically include a finely divided catalyst, such asplatinum, supported on carbon particles and mixed with an ionomer. Theelectrolyte membrane is disposed between the electrodes and is generallyformed from a proton-conducting polymer such as Nafion® polymer,commercially available from E.I. du Pont de Nemours and Company, forexample. The electrolyte membrane and electrodes are disposed betweenporous diffusion media (DM). The DM facilitates a delivery of gaseousreactants, typically hydrogen and oxygen, to the electrodes for anelectrochemical fuel cell reaction. Generally, the catalyst is coated onthe electrolyte membrane (CCM) to form a membrane-electrode-assembly(MEA). In another typical configuration, the DM is catalyst-coated(CCDM) to form the electrodes of the fuel cell.

The electrolyte membrane, electrodes, and DM are disposed between a pairof fuel cell plates and sealed with a gasket. When the electrolytemembrane, electrodes, and DM are assembled as a unit, for example, withother components such as the gasket and the like, the assembly is calleda unitized electrode assembly (UEA).

Each fuel cell plate has an active region to which the gaseous reactantsare delivered for distribution to the electrodes. The fuel cell platealso includes a feed region having flow channels configured to deliverthe gaseous reactants from a supply source to the active region. Theelectrolyte membrane typically extends across the feed region andterminates at the gasket. The electrolyte membrane is employed toseparate and inhibit an intermixing of the gaseous reactants. However,the DM is generally limited to the active region so that there isadequate space for the gaseous reactants to flow through the flowchannels in the feed region. The fuel cell may also include metal shimsor foils in the feed region that provide a stiffness to the electrolytemembrane and that militate against a blockage of the flow channels bythe membrane.

The electrolyte membrane in the feed region is typically coated orlaminated with a chemically inert material to inhibit a corrosion of thefuel cell plates that contact the electrolyte membrane. However, boththe electrolyte membrane and the inert materials are prone to swelling.Swelling of the electrolyte membrane is known to cause flow channelblockage, delamination from the metal shims, and result in fuel cellinstability. The electrolyte membrane also is generally not compatiblewith certain fuel cell or automotive fluids, such as coolants, grease,and oil, with which the electrolyte membrane may come into contactduring operation. The electrolyte membrane that extends into the feedregion or to an outer perimeter of the fuel cell is particularlysusceptible to contamination with these types of fluids.

There is a continuing need for a fuel cell having an electrolytemembrane with optimized dimensions. Desirably, the optimized membranedimensions increase fuel cell robustness and reliability. The optimizedelectrolyte membrane also desirably reduces the fuel cell complexity andcost and improves manufacturability of the fuel cell.

SUMMARY OF THE INVENTION

In concordance with the instant disclosure, a UEA that has anelectrolyte membrane not substantially disposed in the feed region of afuel cell, increases the fuel cell robustness and reliability bymilitating against flow channel blockage and corrosion of the fuel cellplate, and reduces the fuel cell manufacturing complexity and cost, issurprisingly discovered.

In one embodiment, a UEA is employed in a fuel cell having an activeregion and a feed region. The UEA includes an electrolyte membranedisposed between a pair of electrodes. The electrolyte membrane and thepair of electrodes are disposed between a pair of DM. The electrolytemembrane, the pair of electrodes, and the DM are configured to bedisposed adjacent the active region of the fuel cell. A barrier layercoupled to the electrolyte membrane is configured to be disposedadjacent the feed region of the fuel cell.

In a further embodiment, a fuel cell includes the UEA disposed between apair of fuel cell plates. Each of the fuel cell plates has an activeregion and a feed region. The electrolyte membrane, the electrodes, andthe DM are disposed adjacent the active region. The barrier film isdisposed adjacent the feed region. The dimensions of the electrolytemembrane are thereby optimized.

In another embodiment, a plurality of the fuel cells with the optimizedelectrolyte membrane may be stacked to form a fuel cell stack. The fuelcell stack has an enhanced robustness and reliability.

DRAWINGS

The above, as well as other advantages of the present disclosure, willbecome readily apparent to those skilled in the art from the followingdetailed description, particularly when considered in the light of thedrawings described hereafter.

FIG. 1 is illustrates a schematic, exploded perspective view of a PEMfuel cell stack with barrier film according to the present disclosure,showing only two cells;

FIG. 2 a is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered between a pair of DM and a joint film, the barrier filmoverlapping an electrolyte membrane and a joint film;

FIG. 2 b is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered between a pair of DM, the barrier film overlapping anelectrode and an electrolyte membrane;

FIG. 2 c is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered between a DM and a catalyst coated DM, the barrier filmdisposed between a catalyst coated DM and an electrolyte membrane;

FIG. 2 d is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered between pair of catalyst coated DM, the barrier filmdisposed between an catalyst coated DM and an electrolyte membrane;

FIG. 3 a is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered between a pair of DM, the barrier film disposed between apair of joint films;

FIG. 3 b is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered between a pair of DM, the barrier film overlapping a singlejoint film;

FIG. 4 a is a fragmentary, cross-sectional view of a UEA with a barrierfilm disposed outside of the DM, the barrier film disposed between apair of joint films;

FIG. 4 b is a fragmentary, cross-sectional view of a UEA with a barrierfilm disposed outside of the DM, the barrier film overlapping a singlejoint film;

FIG. 5 a is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered on a single DM, the barrier film overlapping an electrolytemembrane disposed between a pair of joint films;

FIG. 5 b is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered on a single DM and a joint film, the barrier filmoverlapping an electrolyte membrane and the joint film;

FIG. 5 c is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered on a single DM, the barrier film overlapping an electrolytemembrane and a joint film; and

FIG. 5 d is a fragmentary, cross-sectional view of a UEA with a barrierfilm layered on a single DM, the barrier film overlapping an electrodeand an electrolyte membrane.

DETAILED DESCRIPTION OF THE INVENTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould also be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

FIG. 1 depicts an exemplary fuel cell stack 2 according to the presentdisclosure. The fuel cell stack 2 has a pair of MEAs 4, 6 separated fromeach other by an electrically conductive bipolar plate 8. Although MEAs4, 6 of a CCM design are shown for purpose of simplicity, it should beunderstood that the fuel cell stack 2 may employ a CCDM design ifdesired.

The bipolar plate 8 has an active region 9 and a feed region 10. Thebipolar plate 8 may have a nested plate design, for example, as isdescribed in U.S. Pat. No. 6,974,648 and in U.S. Pat. App. Pub. No.200610127706, the disclosures of which are incorporated herein byreference in their entireties. For simplicity, only a two-cell stack(i.e. one bipolar plate) is illustrated and described in FIG. 1, itbeing understood that the typical fuel cell stack 2 will have many moresuch cells and bipolar plates.

The MEAs 4, 6, and particularly the electrolyte membranes of the MEAs 4,6, have optimized or “thrifted” dimensions that do not extendsubstantially beyond the active region 9. For example, the MEAs 4, 6 aresubstantially limited to the locations of the fuel cell stack 2electrochemical reactions. It should be understood that the MEAs 4, 6may be optimized on all edges, or on select edges, as desired.

The MEAs 4, 6 and bipolar plate 8 are stacked together between a pair ofclamping plates 11, 12 and a pair of unipolar end plates 14, 16. Theclamping plates 11, 12 are electrically insulated from the end plates14, 16 by a gasket or a dielectric coating (not shown). The unipolar endplates 14, both working faces of the bipolar plate 8, and the unipolarend plate 16 include flow fields 18, 20, 22, 24. The flow fields 18, 20,22, 24 distribute reactants, such as hydrogen gas, for example, from acompressed hydrogen source or a reformate, and oxygen, for example, fromair over an anode and a cathode, respectively, of the MEAs 4, 6.

Nonconductive gaskets 26, 28, 30, 32 provide seals and an electricalinsulation between the several components of the fuel cell stack 2.Gas-permeable DM 34, 36, 38, 40 abut the anodes and the cathodes of theMEAs 4, 6. The end plates 14, 16 are disposed adjacent the DM 34, 40,respectively, while the bipolar plate 8 is disposed adjacent the DM 36on the anode face of MEA 4. The bipolar plate 8 is further disposedadjacent the DM 38 on the cathode face of MEA 6.

Barrier films 42, 44 are positioned between the MEAs 4, 6 and thenonconductive gaskets 26, 28, 30, 32. The barrier films 42, 44 aredisposed adjacent the feed region 10 of the bipolar plate 8. The barrierfilms 42, 44 are electrically nonconductive. The MEAs 4, 6 are coupledto the barrier films 42, 44. The barrier films 42, 44 may also becoupled to the nonconductive gaskets 26, 28, 30, 32. In particularexamples, the barrier films 42, 44 may be formed respectively integralwith the nonconductive gaskets 26, 28, 30, 32. The barrier films 42, 44may include at least one seal, for example, molded on the barrier films42, 44 as seal carriers. It should be appreciated that having the sealformed on the barrier films 42, 44 may facilitate the employment offewer components in assembling the fuel cell stack 2.

The bipolar plate 8, unipolar end plates 14, 16, and the gaskets 26, 28,30, 32 each include a cathode supply aperture 72 and a cathode exhaustaperture 74, a coolant supply aperture 75 and a coolant exhaust aperture77, and an anode supply aperture 76 and an anode exhaust aperture 78.Supply manifolds and exhaust manifolds of the fuel cell stack 2 areformed by an alignment of the respective apertures 72, 74, 75, 77, 76,78 in the bipolar plate 8, unipolar end plates 14, 16, and the gaskets26, 28, 30, 32. The hydrogen gas is supplied to an anode supply manifoldvia an anode inlet conduit 80. The air is supplied to a cathode supplymanifold of the fuel cell stack 2 via a cathode inlet conduit 82. Ananode outlet conduit 84 and a cathode outlet conduit 86 are alsoprovided for an anode exhaust manifold and a cathode exhaust manifold,respectively. A coolant inlet conduit 88 is provided for supplyingliquid coolant to a coolant supply manifold. A coolant outlet conduit 90is provided for removing coolant from a coolant exhaust manifold. Itshould be understood that the configurations of the various inlets 80,82, 88 and outlets 84, 86, 90 in FIG. 1 are for the purpose ofillustration, and other configurations may be chosen as desired.

The barrier films 42, 44 are employed to separate the hydrogen gas andthe air supplied to the fuel cell stack 2 in the feed region 10,particularly since the optimized MEAs 4, 6 are limited substantially tothe active region 8. It is surprisingly found that joint configurationsfor the MEAs 4, 6 and barrier films 42, 44, as described in variousembodiments hereinafter, militate against a separation of the MEAs 4, 6and the barrier films 42, 44 under typical fuel cell stack 2 operatingconditions. The joint configurations may be employed to reliably couplethe MEAs 4, 6 and the barrier films 42, 44, thereby enabling the use ofoptimized electrolyte membrane dimensions. At least one of bonding, suchas with a chemical adhesive, fusing, and compression may be employed tofurther couple the MEAs 4, 6 and the barrier films 42, 44 under thejoint configurations described.

In the various exemplary joint configurations shown in FIGS. 2 a to 5 d,a UEA 200 of the fuel cell stack 2 may include a barrier layer 202, anelectrolyte membrane 204, a first electrode 206, a second electrode 208at least one of a first joint film 210 and a second joint film 212, afirst DM layer 214, and a second DM layer 216. The first electrode 206and the second electrode 208 may be bonded to either the membrane 204 ina CCM configuration or one of the DM layer 214, 216 in a CCDMconfiguration as desired. Combinations of the joint configurations shownin FIGS. 2 a to 5 d, for example, having one configuration along thefeed region 9 and another configuration along the active region 10 mayalso be employed. A skilled artisan should appreciate that the jointconfigurations described are for the purposes of illustration and thatother suitable joint configurations may be selected as desired.

The barrier layer 202 corresponds substantially to one of the barrierfilms 42, 44 shown in FIG. 1. The barrier layer 202 is formed from amaterial that does not substantially swell or degrade with exposure tothe fuel cell reactants and automotive fluids, such as coolant, oil, andgrease. In particular, the barrier film 202 is formed from a materialthat is able to provide both electrical and mechanical separation. Thebarrier layer 202 may also be formed as a unitary layer to militateagainst delamination. As a nonlimiting example, the barrier layer 202 isformed from one of a polyethylene naphthalate (PEN), a polyethyleneterephthalate (PET), and a polyimide polymer such as Kapton® polymercommercially available from E. I. du Pont de Nemours and Company, forexample. It should be understood that other suitable polymeric materialsfor the barrier layer 202 may be selected as desired.

The electrolyte membrane 204, the first electrode 206, and the secondelectrode 208, when assembled, correspond substantially to one of theMEAs 4, 6 described in FIG. 1. The first and second DM layers 214, 216correspond substantially to the DMs 36, 38 disclosed in FIG. 1.

Referring now to FIGS. 2 a to 2 d, first, second, third, and fourthjoint configurations, where the barrier layer 202 overlaps theelectrolyte membrane 204 to form a joint 218, respectively, are shown.Both the first DM layer 214 and the second DM 216 layer overlap thejoint 218 in FIGS. 2 a to 2 c.

In the first joint configuration shown in FIG. 2 a, an exposed portion220 of the electrolyte membrane 204 extends beyond the first and secondelectrodes 206, 208. The exposed portion 220 thereby provides anon-coated surface for coupling to the barrier layer 202. The barrierlayer 202 is disposed on at least a portion of the electrolyte membrane204 and may be bonded, for example, as described hereinabove. The firstjoint film 210 covers and seals an end of the first electrode 206 andthe electrolyte membrane 204. As the first and the second electrodes206, 208 are separated by the first joint film 210 and the barrier layer202, respectively, contact between one of the electrodes 206, 208 andthe opposing DM 214, 216 is inhibited. A short circuit is therebymilitated against.

The barrier layer 202, the electrolyte membrane 204, the first andsecond electrodes 206, 208, and the joint film 210 are layered betweenthe first DM 214 and the second DM 216. The first DM 214 and the secondDM 216 overlap the joint configuration. The first and second DMs 214,216 provide a mechanical pressure on the barrier layer 202 and theelectrolyte membrane 204 when the fuel cell stack 2 is placed undercompression during an assembly thereof. In particular embodiments, themechanical pressure is sufficient to couple the barrier layer 202 andthe electrolyte membrane 204 with or without a supplemental bonding suchas by bonding with a chemical adhesive.

As shown in the second joint configuration of FIG. 2 b, both theelectrolyte membrane 204 and the second electrode 208 are disposed on aportion of the barrier layer 202. The barrier layer 202 is disposedbetween the second electrode 208 and the second DM 216. The exposedportion 220 of the electrolyte membrane 204 that extends beyond thefirst and second electrodes 206, 208 is coupled to the barrier layer202.

With reference to FIG. 2 c, the third joint configuration includes thebarrier layer 202 disposed between the second electrode 208 and theelectrolyte membrane 204. It should be recognized that the second andthird joint configurations do not employ the first and second jointfilms 210, 212, and therefore, may have a reduced manufacturingcomplexity.

In FIG. 2 d, the fourth joint configuration includes the barrier layer202 disposed between the first DM 214 and the electrolyte membrane 204.The first DM 214 is catalyst coated to form the first electrode 206. Thesecond DM 216 is also catalyst coated to form the second electrode 208and the electrolyte membrane 204 disposed thereon, for example, bybonding before a cutting of the second DM 216. An edge of each of theelectrolyte membrane 204, the electrodes 206, 208, and the DM 214, 216are also aligned in the fourth joint configuration shown.

Exemplary fifth and sixth joint configurations are shown in FIGS. 3 aand 3 b, respectively. In the fifth and sixth joint configurations, thebarrier layer 202 overlaps at least one of the first and second jointfilms 210, 212. At least one of the first and second joint films 210,212 is further disposed on the exposed portion 220 of the electrolytemembrane 204. The first DM 214 and the second DM 216 sandwich the joint218 formed by the overlapping of the barrier layer 202 and at least oneof the first and second joint films 210, 212.

In the fifth joint configuration shown in FIG. 3 a, the exposed portion220 of the electrolyte membrane 204 and the barrier layer 202 arelayered between the first and second joint films 210, 212. The firstjoint film 210 is disposed above the electrolyte membrane 204 and thebarrier layer 202 and is further disposed adjacent the first electrode206. The second joint film 212 is disposed below the electrolytemembrane 204 and the barrier layer 202 and is further disposed adjacentthe second electrode 208. The ends of the first and second electrodes206, 208 are sealed, respectively, by the first and second joint films210, 212.

In FIG. 3 b, the sixth joint configuration includes an overlapping ofthe first joint film 210 with each of the first electrode 206, theexposed portion 220 of the electrolyte membrane 204, and the barrierlayer 202.

Seventh and eighth joint configurations are shown in FIGS. 4 a and 4 b.The seventh and eighth joint configurations include the barrier layer202 disposed outside of the first DM 214 and the second DM 216. In FIG.4 a, the first and the second joint films 210, 212 are disposed on thefirst and second electrodes 206, 208, respectively, and the exposedportion 220 of the electrolyte membrane 204. The exposed portion 220terminates substantially at edges 222, 224 of the first DM 214 and thesecond DM 216, respectively. The first and second joint films 210, 212extend beyond the first and second DMs 214, 216 and sandwich the barrierlayer 202.

In the eighth joint configuration shown in FIG. 4 b, only the firstjoint film 210 overlaps a portion of the barrier layer 202 film outsideof the first DM 214 and the second DM 216. The first and second DMs 214,216 may be compressed at the edges 222, 224 thereof with the first jointfilm 210 to seal the exposed portion 220 of the electrolyte membrane204.

As the barrier layer 202 is not covered by the first and second DMs 214,216, the joint films 210, 212 may be bonded to the barrier layer 202 bymeans other than compressive force. A thickness of the barrier layer 202in the seventh and eighth joint configurations may be greater than whenthe barrier layer 202 is layered between the DMs 214, 216. The thickerbarrier layer 202 provides an improved stiffness that militates againstblockage of flow channels in the feed regions 10 of the fuel cell stack2. A skilled artisan should also appreciate that suitable thicknessesmay vary with the fuel cell stack 2 design, and may be employed asdesired.

Referring now to FIGS. 5 a to 5 d, exemplary ninth, tenth, eleventh, andtwelfth joint configurations for the UEA 200 are shown, respectively.The barrier layer 202 is disposed in-line with one of the first DM 214and the second DM 216. In a particular embodiment, the barrier layer 202has a thickness that is substantially the same as a thickness of one ofthe first and second DM 214, 216. It should be understood that, havingsubstantially the same thickness as the in-line DM 214, 216, acompressive force may be provided that is sufficient to seal the joint218 between the barrier layer 202 and the electrolyte membrane 204, withor without supplemental bonding.

In the ninth joint configuration shown in FIG. 5 a, the barrier layer202 is disposed in-line with the first DM 214. A portion of the barrierlayer 202 is layered with each of the first joint film 210, the exposedportion 220 of the electrolyte membrane 204, and the second DM 216. Thefirst joint film 210 and the second joint film 212 sandwich the assemblyof the first electrode 206, the electrolyte membrane 204, and the secondelectrode 208. The first and second joint films 210, 212 seal the firstand second electrodes 206, 208, respectively.

The tenth joint configuration of FIG. 5 b includes the barrier layer 202disposed in-line with the second DM 216. The barrier layer 202 islayered with the exposed portion 220 of the electrolyte membrane 204 andthe first DM 214. The second electrode 208 terminates substantially atthe edge 224 of the second DM 216.

In the eleventh joint configuration shown in FIG. 5 c, a portion of thebarrier layer 202 is disposed on each of the first joint film 210, theexposed portion 220 of the electrolyte membrane 204, and the second DM216. The eleventh configuration does not include the second joint film212.

With reference to FIG. 5 d, the barrier layer 202 is disposed in-linewith the first DM 214. A portion of the barrier layer 202 is furtherdisposed on each of the first electrode 206, the electrolyte membrane204, and the second DM 216. The twelfth joint configuration according toFIG. 5 d does not employ the joint films 210, 212. It should beappreciated that the joint configurations of FIGS. 5 c and 5 d,employing one or none of the joint films 210, 212, provides for lessmanufacturing complexity in comparison to the joint configurationshaving both joint films 210, 212.

It is surprisingly found that the joint configurations disclosed hereinfacilitate a bond between the barrier layer 202 and the electrolytemembrane 204 that allows the dimensions of the electrolyte membrane 204and the electrodes 206, 208 to be optimized. In particular embodiments,the electrolyte membrane 204 does not extend substantially into the feedregion 10 of the fuel cell stack 2. Thus, the electrolyte membrane 204does not become contaminated with fuel cell and automotive fluids suchas coolant, grease, and oil, which the fuel cell stack 2 may be exposedto in operation.

A skilled artisan should appreciate that at least one of the barrierlayer 202 and the joint films 210, 212 of the present disclosure,depending on the joint configuration selected, may also militate againsta degradation of the electrolyte membrane 204 caused by the DM 214, 216.For example, the barrier layer 202 and the joint films 210, 212 overlapthe electrolyte membrane 204 and may inhibit a degradation or cutting bythe DM 214, 216 edges 222, 224, when the components are placed undercompression.

Various joint configurations according to the present disclosure mayfurther minimize a volume necessary to form the bond, due to theelimination of supplemental adhesives. In particular embodiments, whenthe DM 214, 216 overlap the joints 218 and the fuel cell stack 2 isplaced under compression, a mechanical pressure sufficient to couple thebarrier layer 202 and the electrolyte membrane 204 is provided. Thecoupling of the exposed portion 220 of the electrolyte membrane 204 tothe barrier layer 202 may also provide a robust seal substantiallyimpervious to the fuel cell stack 2 fluids.

A thickness of the barrier layer 202 may further be selected to militateagainst an undesirable over-compression of the joint 218 or anundesirable reliance on supplement bonding such as by chemical adhesionbetween the barrier layer 202 and the electrolyte membrane 204. Thebarrier layer 202 thickness may be suitable for supporting one or morepolymeric seals. The barrier layer 202, having a suitable thickness,also provides an improved stiffness to the feed region 10. The barrierlayer 202 may militate against a blockage of flow channels in the feedregions 10 of the fuel cell stack 2, particularly if the barrier layer202 is not otherwise supported, for example, with a metal shim. Thebarrier layer 202 minimizes to flow channel intrusions and theaccompanying flow maldistribution throughout the fuel cell stack 2.

It should be appreciated that the barrier layer 202 is employed as aflow support for the hydrogen gas and the air because the gases flowthereover and are transported to and from the fuel cell stack 2 alongthe barrier layer 202. As the hydrogen gas and the air flow thereover,the substantially impermeable barrier layer 202 also advantageouslyresists a crossover and intermixing of the hydrogen gas and the air. Thebarrier layer 202 also militates against a short circuit of the fuelcell stack 2, for example, by providing an insulating layer between atleast one of the first and second electrodes 206, 208, the first andsecond DM 214, 216, the first electrode 206 and the second DM 216, thesecond electrode 208 and the first DM 214, and the plates of the fuelcell stack 2, such as between bipolar plate 8, and one of the unipolarplates 14, 16.

It should also be understood that the optimized dimensions of theelectrolyte membrane 204, which are facilitated by the jointconfigurations of the present disclosure, allows for an efficient use ofthe electrolyte membrane 204 materials. A quantity of the electrolytemembrane 204 material employed according to the present disclosure maybe minimized. Illustratively, electrolyte membrane 204 material along atleast one of the active region 9 and the feed region 10 may be replacedwith the barrier layer 202. Additionally, as the electrolyte membranes204 may not extend substantially into the feed regions 10 of the fuelcell stack 2, additional protective coatings and layers are not requiredto militate against corrosion of the bipolar plate 8, and unipolarplates 14, 16.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes may be made without departingfrom the scope of the disclosure, which is further described in thefollowing appended claims.

What is claimed is:
 1. A unitized electrode assembly for a fuel cellhaving an active region and a feed region, the unitized electrodeassembly comprising: an electrolyte membrane disposed between a pair ofelectrodes, the electrolyte membrane and the pair of electrodes disposedbetween a pair of diffusion media and configured to be disposed at theactive region of the fuel cell, wherein the electrolyte membrane isconfigured to not extend substantially into the feed region; and abarrier layer coupled to the electrolyte membrane, the barrier layerconfigured to be disposed at the feed region of the fuel cell and toextend at least partly into the active region of the fuel cell, whereinthe barrier layer is disposed on and abutting but not impregnating atleast a portion of the electrolyte membrane and only one of theelectrodes, and the barrier layer is disposed between the electrolytemembrane and both of the electrodes.
 2. The unitized electrode assemblyof claim 1, wherein at least one of the pair of electrodes extends to anedge of the electrolyte membrane.
 3. The unitized electrode assembly ofclaim 1, wherein the barrier layer is formed from at least one of apolyethylene terephthalate (PET), a polyethylene naphthalate (PEN), anda polyimide polymer.
 4. The unitized electrode assembly of claim 1,wherein the pair of diffusion media is catalyst coated to form the pairof electrodes.
 5. The unitized electrode assembly of claim 1, wherein anedge of the electrolyte membrane and an edge of the pair of electrodesalign with an edge of the pair of diffusion media.
 6. The unitizedelectrode assembly of claim 1, wherein the barrier layer overlaps theelectrolyte membrane, the barrier layer and the electrolyte membrane areconfigured to form a joint.
 7. The unitized electrode assembly of claim6, wherein the joint is configured to facilitate a bond between thebarrier layer and the electrolyte membrane.